It’s not the size of your microstock portfolio that counts when you’re looking to maximize your revenues, says Fotolia’s President and co-founder, it’s the quality of the images they contain.

“There are photographers who have big portfolios but don’t sell,” Oleg Tscheltzoff told us from Paris. “[But] if you have just two fantastic images, even one, you will make money. People will find you. A great image online will start to sell immediately.”

And a quick browse of the site suggests that it could keep selling too. This Photoshopped image of an eye, for example, has been downloaded an impressive 1,173 times on Fotolia while this shot of a jumping goldfish has sold 1,132 licenses. Even at just a dollar a piece, with top photographers taking up to 80 percent of the sales price, that’s still a lot of money earned by one image.

It helps that Fotolia’s search system is weighted: although new photos appear at the top of search results, leaving older and unsold images to sink into the site, high image views and lots of sales can ensure that the best photos are always shown to buyers, leading to even more downloads.

The existence of large portfolios with few sales though might suggest that Fotolia’s selection procedure could do with some better filtering (“As long as our moderators think the picture is a good commercial image and has potential then we take it,” says Oleg) but the result is a microstock site with plenty to offer buyers. Founded in 2005, Fotolio now has over two million images online. More than 50,000 photographers have supplied photos, the site boasts more than half a million members, and — most importantly — sells over 10,000 photos a day.

According to Oleg, Fotolia has about fifteen photographers earning over $200,000 a year from their photos and “hundreds just one league under but who are extremely good.”

“We have a lot of professionals,” Oleg explained. “They make a lot of money. But we are also open to semi-pro and some very good amateurs. Some people make thousands every month. For them it’s a profession [and] they shoot professional images every day.”

Andres Rodriguez, one of Fotolia’s highest-selling photographers, for example, says that he tries to upload at least 500 images each month. “[Each photo] takes me between ten minutes and two hours,” he explained. “If you look at my work you see I do lots of compositions, they take a lot longer to produce than a person’s portrait but that’s where I have fun!” And for him, that sort of effort pays off. Andres gets about 30,000 downloads a month.

To earn the highest incomes at microstock sites like Fotolia then, pictures have to be professional quality and the photographer has to treat the shoots as a professional business. Oleg pointed out that business images and photos with models are most likely to be downloaded (“Images with people inside sell much more,” he said) and photographers can also market their portfolio themselves.

“Once the portfolio is on Fotolia, it also has its own URL so if the photographer has his own blog or whatever, he can promote these images by himself,” Oleg recommended.

Get all that right and send buyers to your pictures, and you could have the perfect microstock combination: a large portfolio filled with high-quality, high-earning images.